1. Field of the Invention
This invention relates to stepper motors, and more particularly, to stepper motors in which the motion of an armature closing a gap against a pole of an electromagnet is transferred by mechanical means into a cumulative rotational output.
2. Background Information
Stepper motors are electromechanical devices having a rotor driven in discrete steps by the application of electrical current to various coils. In this way, a stepper motor may be driven through multiple revolutions or through a fraction of a revolution. Generally, the sustained application of current to one or more selected coils results in the rotor being held in a fixed position, while the application of current to the coils in accordance with a specific sequence results in continuous rotation of the rotor.
One type of conventional stepper motor has a rotor, having a plurality of magnetic poles formed in permanent magnets, rotating within a stator, having a number of electromagnetic coils, which are pulsed in sequence to effect rotation of the rotor. One significant problem with the conventional stepper motor described above is the difficulty in stopping the stepper motor. This problem is a result of the fact that the coils are maintained in an energized condition to stop and hold the rotor at a predetermined angle and the resulting magnetic field tends to act as a spring system attached to the rotor. The result is an overshoot condition and subsequent vibrations caused by the inertia of the rotor and of the driven load.
The above problems associated with the dynamic response may be alleviated through the use of complex circuitry to slow the motor before stopping. Alternately, the problems may be overcome by designing a completely different type of stepper motor, in which rotation of the rotor is effected by the closure of an armature to the pole of an electromagnet and a separate mechanism is provided to transfer the armature motion into rotation of the rotor.